1. Field of the Invention
The present invention relates to a control apparatus for camera and more particularly relates to a control apparatus provided with an electric motor for driving a mechanism including a diaphragm device and a shutter device.
2. Related Background Art
In the art of the camera with built-in motor(s), many attempts have been made to realize a further reduction of size, weight and manufacturing cost of the camera. In order to attain the objects, it is desirable to use one and the same motor as a single driving source for all of the driving systems in the camera. In a prior art camera of the type in which a motor is used as a single driving source for all of the driving systems, there is generally provided an interlocking mechanism by which a film take-up mechanism and a shutter-charging mechanism are interlocked to drive the two different mechanisms in one and the same step.
Furthermore, in case of the single lens reflex camera having a turn-up mirror, three different mechanisms must be driven by a single motor at the same step. In this type of camera, the turn-up mirror is normally locked in the position for through-finder observation by a lock member. In a first step of an exposure operation, the turn-up mirror is released from the lock member's hold. A spring is used as a driving source for the turn-up mirror. Therefore, in addition to the driving of the above-mentioned film take-up mechanism and the shutter-charging mechanism, the spring for driving the turn-up mirror must be charged at the same step. In other words, three different mechanisms must be concurrently driven by a single motor during the same step.
As a matter of course, a large load is applied to the motor at the same time. To bear the large load, a high power motor must be used. The use of a large and high power motor naturally increases the consumption of electric current. This is against the purpose of a small size, light weight and power saving camera.
The problem which the prior art has tried to solve is, therefore, how to disperse the driving force and how to decrease the load on the single motor.
It has been found undesirable to drive the mirror system and the film take-up device by one and the same motor. In this case, one or more clutch mechanisms are needed, which renders the mechanism in the camera unduly complicate.
Regarding the aperture control, there are known many difficult problems. For example, when a flash light exposure is to be performed, it is necessary to preset an aperture value and a shutter time suitable for flash light exposure. This presetting operation is not only troublesome to the user of the camera but also leads to setting errors very often.
The presetting of an aperture value for flash light exposure is complicated further by the fact that the aperture value must be determined taking into account the guide number etc. of the flash device then used. Such a flash device has been known which is provided with the function to automatically adjust the intensity of the flash light by measuring the reflected light from the object. Even when one carries out a flash light exposure using such an automatic flash device, it is necessary to manually preset an aperture value considering the characteristics of the flash device. Moreover, it is required to preset an aperture value or change a preset aperture value in accordance with the sensitivity of the film then used. All of these setting operations trouble the users and lead them to setting errors.
The shutter mechanism also involves some problems. Recently, the driving system of the shutter mechanism has been simplified for the above-mentioned purpose. In this simplified type of shutter device, the shutter blades before running are anchored by a magnetic attraction. More specifically, there is used a shutter blade driving arm provided with a piece of iron which is directly attracted by an electromagnet to hold the shutter blades in the start position. To move the arm toward the electromagnet there is provided a charge member in the camera. Prior to exposure, the charge member must be retracted to a position apart from the arm. This retraction of the charge member often causes troubles. If the charge member is rapidly retracted, the arm can not be anchored well by the attraction of the electromagnet. In this case, the shutter blades accidentaly start running together with the charge member.